1. Field of the Invention
The present invention relates to a reference electrode and an automatic electrochemical potential correction apparatus using the same, and, more particularly, to a reference electrode including an electrolyte containing an optically-active material, which can maintain accuracy for a long period of time in the electrochemical measurement, and an automatic electrochemical potential correction apparatus using the same.
2. Description of the Related Art
In order to measure and control chemical or electrochemical reactions occurring in liquid media, such as aqueous solutions, organic solutions, high-temperature molten salts and the like, electrochemical methods have been widely used from the late 19th century up to the present. Particularly, from the late 20th century, research and development in the field of secondary lithium batteries, fuel cells and solar cells has been enlarged, so that the demand for using the electrochemical methods is increasing rapidly.
In the electrochemical methods, in order to accurately measure and control the potential of a working electrode, it is necessarily required to use a reference electrode. Generally, the reference electrode is fabricated using an electrode reaction in which an oxidation-reduction reaction appears clearly in a narrow potential region.
Typical electrode reactions used to fabricate a reference electrode are as follows (Bard, A. J. & L. R. Faulkner, Electrochemical Methods: Fundamentals and Applications. New York: John Wiley & Sons, 2nd Edition, 2000).
2H++2e−⇄H2 (Pt); Standard hydrogen electrode (SHE) (E°=0.0V)
AgCl+e−⇄Ag+Cl−; Silver-Silver Chloride Electrode (E°=0.225V saturated)
Hg22++2e−⇄2Hg, Hg22++2 Cl−⇄Hg2Cl2; Saturated calomel electrode (SCE) (E°=+0.242V saturated)
Cu2++2e−⇄Cu; Copper-copper(II) sulfate electrode (E°=−0.318V)
Among the electrode reactions, although the first electrode reaction, which is a reduction reaction of hydrogen ions to hydrogen gases, is a standard reaction (E°=0.0 V), it is scarcely used practically because hydrogen gases must be treated.
FIG. 1 is a sectional view showing a conventional reference electrode.
Referring to FIG. 1, the conventional reference electrode includes an electrode body provided at the end thereof with an electrolyte separation membrane 11, an inner electrode 20 provided in the electrode body, and an electrolyte 30 charged in the electrode body such that the inner electrode 20 is partially immersed therein.
Generally, in a reference electrode most frequently used in the field of research and industries, the inner electrode 20 is an Ag/AgCl electrode or a calomel electrode. In this reference electrode, since it is required that the activity of chlorine ions (Cl−) in the electrolyte 30 be constant, the concentration of chlorine ions (Cl−) in the electrolyte 30 must also be maintained constant.
When natural water including underground water and river water or cooling water used in a heat exchanger system is monitored for a long period of time using an electrochemical measurement method, the reference potential of the reference electrode used in this monitoring can be gradually changed because the concentration of an electrolyte containing chlorine ions in the reference electrode is decreased due to the difference in concentration between the electrolyte and a test solution. Further, when the reference electrode is used to monitor natural water or cooling water for a long period of time, the reference electrode is damaged, so that the electrolyte charged in the reference electrode is contaminated, thereby providing an incorrect reference potential.
Korean Patent Registration No. 10-0477448-0000 (2005.03.09) discloses a microvalve for nanofluid flow control using a shape-memory alloy film, in which the microvalve is installed in an electrode system, thus minimizing the consumption of KCl (Cl−). Further, Korean Patent Registration Nos. 10-0329393-0000 (2002.03.07) and 10-0483628-0000 (2005.04.07) disclose a reference electrode, in which the leakage of KCl present in the reference electrode is prevented by using a polymer material, thus improving the durability of the reference electrode. Furthermore, Korean Patent Registration No. 10-0612270-0000 (2006.08.07) discloses a reference electrode for high-pressure and high-temperature aqueous environments, in which the concentration of KCl is maintained constant by using a polymer electrolyte, and which constitutes an electrode system such that it can be used in high-pressure high-temperature aqueous environments.
In order to improve the stability of a reference electrode, the leakage of an electrolyte charged in the reference electrode may be minimized, or a device for automatically circulating the electrolyte may be installed in the reference electrode.
In an Ag/AgCl electrode, in order to recover silver chloride (AgCl), an oxidation current or potential is periodically applied to the Ag/AgCl electrode, thus regenerating the surface thereof.
U.S. Pat. No. 4,822,456 (1989.04.18) discloses a method of preventing the contamination of a reference electrode by forming junction in the reference electrode using a permeable membrane, and an apparatus for monitoring the contamination of an electrolyte charged in the reference electrode by measuring the change in potential between the inner and outer electrodes provided at the inside and outside of the junction.
PCT Publication Nos. WO 89/07758 (1989.08.24) and PCT/US 89/00628 (1989.02.15), and Korean Patent Registration Nos. 10-0152426-0000 (1998.06.26), 10-0411715-0000 (2003.12.05) and 10-0439645-0000(2004.06.30) disclose a technology of miniaturizing a reference electrode using a thin film technique in order to apply the reference electrode to the semiconductor field.
As described above, to date, the technical improvement in the field of a reference electrode has been accomplished by preventing the leakage of an electrolyte charged in the reference electrode or by miniaturizing the reference electrode. However, there has been no attempt to improve the stability of a reference electrode and monitor the state of the reference electrode by adding a light-absorbing material to an electrode and then correcting the concentration of the electrolyte using a spectrometer in order to detect the change in concentration of the electrolyte, which influences the electrode reaction of the reference electrode.